Gravitational lens. Diagram showing how light rays from distant stars are bent as they pass through the gravitational field of the Sun. This happens for light rays that pass close to the edge of the Sun, leading to a change in the apparent position of the stars near to the edge of the Sun or behind the Sun. This effect can be viewed during an eclipse (shown here), and measurements of this effect taken during an eclipse in 1919 helped lead to acceptance of Einstein's theory of General Relativity. The grid represents space-time. In Einstein's theory, gravity is the warping of space-time by mass.